Energy Changes

Created by

Nazmine

Cards (44)

Energy profile diagram for an exothermic reaction
Label the axis: energy
Label the reactants and products
Label the activation energy
Label the energy change
Bonds 
Contain two chemical symbols separated by either a single, double or triple line
The chemical symbols can be the same or they could be different
Identifying bonds 
Count the number of each band you can repeatedly see
The number at the front of a molecule tells you there are 'X' number of the molecules present in the reaction (X is any number)
Bond Energy Calculations 
Can be used to explain why energy changes take place
Old bonds are broken in reactants
New bonds are formed in products
Breaking chemical bonds 
Energy is supplied (taken in), therefore this is an endothermic process
Forming new bonds 
Energy is released, therefore this is an exothermic process
Bond energies are always positive
Bond energies are measured in kJ/mol
Calculating overall energy change
Difference between the sum of the energy needed to break bonds in the reactants and the sum of the energy released when bonds in the products are formed
What happens to energy during chemical reactions?
Energy is transferred to or from surroundings
What is an exothermic reaction?
It is accompanied by a temperature rise
Give an example of an exothermic reaction.
Combustion
How are exothermic reactions used in products?
They are used in self-heating cans and hand warmers
What characterizes an endothermic reaction?
It is accompanied by a fall in temperature
Provide an example of an endothermic reaction.
Thermal decomposition
What happens in a reversible reaction that is exothermic in one direction?
It is endothermic in the opposite direction
What is the independent variable in the required practical?
The metal used
What is the dependent variable in the required practical?
The temperature change
What are control variables in the experiment?
Type, concentration, and volume of acid
What does measurement uncertainty imply?
There is variability in the results obtained
What correlation should be observed in the experiment?
The more reactive the metal, the greater the temperature change
How is the mean temperature change calculated?
By averaging the recorded temperature changes
What is a key safety consideration in the experiment?
Use eye protection due to corrosive acid
What is an accurate measurement?
Close to the true value
What does it mean for results to be precise?
Results are all close together
What does repeatability of results indicate?
Similar results from the same experimenter
What does reproducibility of results indicate?
Similar results from different experimenters
What is activation energy?
The minimum energy needed for a reaction
How do energy level diagrams represent exothermic reactions?
Products have less energy than reactants
How do energy level diagrams represent endothermic reactions?
Products have more energy than reactants
What effect do catalysts have on activation energy?
Catalysts reduce the activation energy needed
What happens to heat energy in exothermic reactions?
It is transferred to the surroundings
What happens to heat energy in endothermic reactions?
It is taken in from the surroundings
How can energy changes in reactions be measured?
By mixing reactants in an insulated container
What is required to break a chemical bond?
Energy is required to break a bond
What happens when a new chemical bond is formed?
Energy is given out
What determines if a reaction is endothermic or exothermic?
Comparison of energy required and released
What are the characteristics of endothermic and exothermic reactions?
Exothermic:
Temperature rises
Heat energy is released
Examples: combustion, rusting, neutralisation
Endothermic:
Temperature falls
Heat energy is absorbed
Examples: thermal decomposition, citric acid and sodium hydrogen carbonate
What are the steps involved in measuring energy changes in a chemical reaction?
Set up equipment
Measure initial temperature
Add reactants and stir
Record highest temperature reached
Calculate temperature change
Repeat with different reactants